Six skills for selecting PCB components
Six skills for selecting PCB components
1. Consider the choice of component package
In the whole schematic drawing stage, we should consider the component packaging and pad pattern decision that need to be made in the layout stage. Some suggestions are given below when selecting components according to the component packaging.
Keep in mind that the package includes the electropneumatic pad connection and mechanical dimensions of the component, i.e. the shape of the component body and the pin of the connecting PCB. Any installation or packaging restrictions that may exist at the top and bottom layers of the final PCB shall be considered when selecting the component.
Some components (such as polar capacitors) may have a high clearance limit that needs to be considered in the component selection process. At the beginning of the design, a basic circuit board frame shape can be drawn. Then place some large or location-critical components (such as connectors) that you plan to use.
In this way, you can see the virtual perspective of the circuit board (without wiring) intuitively and quickly. The relative positioning and height of the circuit board and components are given. This will help to ensure that the PCB components are properly placed in the outer packaging (plastic, chassis, and so on) after assembly. From the tool menu to call the three-dimensional preview mode to browse the entire circuit board.
The pad pattern shows the actual pad or hole shape of the welding device on the PCB. The copper pattern also contains some basic shape information. The size of the pad pattern needs to be correct to ensure the correct welding. Ensure the correct mechanical and thermal integrity of the connected components.
When designing a PCB layout, you need to consider how the circuit board will be manufactured or manually welded. Reflow soldering (flux melting in a controlled high temperature furnace) can handle a wide range of surface mount devices, such as SMD.Wave soldering is commonly used to weld the opposite side of a circuit board to fix a through hole device. But you can also handle some of the table-stickers placed on the back of the PCB.
Generally, when adopting this technique, the underlying surface mount devices must be arranged in a particular direction, and the pad may need to be modified in order to adapt to this type of welding.
You can change the component in the whole process of design choice. Early in the design process will determine which devices should be plated through hole (PTH), which should be used in Surface Mount Technology (SMT) will be helpful to the overall planning of PCB. The factors to be considered are the cost of the device, device availability, area density and power consumption etc..
From a manufacturing point of view, surface mount devices are generally cheaper than through hole devices and generally more usable. For small and medium-sized prototype projects, it is better to select larger surface mount devices or through hole devices, which are not only convenient for manual welding, And is advantageous to check error and debug the process of better connection pad and signal.
2. Use good grounding methods
Ensure that adequate bypass capacitors and ground planes are designed. In the use of integrated circuits, make sure that appropriate decoupling capacitors are used near the power source end to ground (preferably ground plane). The appropriate capacity of the capacitance depends on the specific application, Capacitor technology and operating frequency. When the bypass capacitor is placed between the power supply and the ground pin and is close to the correct IC pin, the electromagnetic compatibility and susceptibility of the circuit can be optimized.
3. Assign virtual component packaging
Print a list of materials to check virtual components. Virtual components are not encapsulated and will not be sent to the layout phase. Create a list of materials and view all virtual components in the design.
The only entries should be power and ground signals, because they are considered virtual components, which are exclusively processed in the schematic environment, and will not be sent to the layout design. Unless used for simulation purposes, the components displayed in the virtual part should be replaced by encapsulated components.
4. Make sure you have complete inventory data
Check to see if there is sufficient complete data in the material list report. After creating the material list report, check carefully to complete the incomplete components, supplier or manufacturer information in all component entries.
5. Sort by component label
To facilitate the sorting and viewing of material lists, ensure that element labels are serially numbered.
6. Checking redundant gates circuit
In general, all redundant gates should have signal connections to avoid empty input ports. Make sure you check all redundant or missing gates, and that all unconnected inputs are fully connected. In some cases, If the input is suspended, the entire system will not work correctly.
If only one of the dual operational amplifier IC components is used, it is recommended that either the other operational amplifier be used, or the input of the unused operational amplifier be terminated and a suitable unit gain (or other gain) feedback network be placed. This ensures that the whole component works properly.
In some cases, an IC with a suspended pin may not be able to work properly within the target range. Usually only when the IC device or other gates in the same device are not working in a saturated state-the input or output is close to or is in the component power rail, The performance of the IC can only meet the requirements of the index. Simulation usually fails to capture this situation because the simulation model does not normally connect multiple parts of the IC together to model the suspension connection effect.